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I'm currently doing a project on magnetic haptic feedback using DC electromagnet. The principle of my haptic feedback system is very simple (figure shown below):

enter image description here

A permanent magnet is stuck to the user's finger (It doesn't necessarily have to be one permanent magnet, here can be multiple permanent magnets stuck to different positions on one finger or even the entire hand). An array of electromagnets surround the permanent magnet and exert electromagnetic force on the permanent magnet in arbitrary magnitude (by changing the magnitude of the current) or direction (by changing the direction of the current). The presumed working space of this system is around 60mm * 60mm * 60mm~150mm * 150mm * 150mm, depending on the performance of the electromagnets. The maximum force exerted should be around 0.5-1N. The electromagnet consists of an iron core and multiple turns of copper wire.

I've currently done some experiments, namely, I tested the magnitude of electromagnetic force on a permanent magnet from one electromagnet by passing an adequate amount of current through its coil. The problem I'm having now, as is expected from electromagnetic theory, is that the magnitude of electormagnetic force decreases way too fast as the distance between the permanent magnet and the electromagnet increases and by the time the permanent magnet reaches the range of the "working space" of this system, there's barely any force left.

Therefore, I'm hoping to increase the magnetic field intensity in the "working space" so that the magnetic force also increases. However, since it's an academic project, I'm trying to explore some more fancy, more novel ways to realize that goal other than the more common, more straightforward ways, namely, increasing the current, increasing the number of turns, increasing the size of the electromagnet...

Therefore I'm hoping you guys can give me some hints or keywords with regard to these potentially fancy methods to increase the magnetic field intensity from a DC electromagnet. DC magnets are preferrable simply it's easier to control but if adopting AC magnets in a certain way can do a better job in this application, the option is still welcomed! I'll be more grateful if you can give me a detailed description about the method you propose!

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    $\begingroup$ Interesting question, but you are up against basic physics for simply increasing the magnetic field intensity from a DC electromagnet. More details might help people better understand the design challenge. How big is the working space that the finger is moving in? What is the biggest force you want to exert on the finger? Can the finger be surrounded on all sides, or just on the bottom as in your sketch? Do the electromagnets have to be DC, or is AC possible? What is the required frequency response of the electromagnets? $\endgroup$ Commented Dec 15, 2022 at 4:26
  • $\begingroup$ @DavidBailey Thanks for your reply! I'll answer your question 1 by 1: 1. The presumed working space of this system is around 60mm * 60mm * 60mm~150mm * 150mm * 150mm, depending on the performance of the electromagnets. 2. The maximum force exerted should be around 0.5-1N (also depending on the performance). 3. Yes, multiple permanent magnets are allowed. 4. DC magnets are preferrable simply it's easier to control but if adopting AC magnets in a certain way can do a better job in this application, the option is still welcomed! 5. I haven't considered freq response since it's a DC magnet. $\endgroup$ Commented Dec 15, 2022 at 8:28
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    $\begingroup$ This is not easy. This video shows 500g levitating (i.e. 5N force) at 8cm from the electromagnets. If you can achieve 1N at 15cm with a small enough magnet on the finger, then to produce controlled lesser forces at closer locations requires determining the position of the finger in real time and then modifying the currents in the electromagnets appropriately. You'd have to worry about the torque, not just the force, on the magnet, and it gets really tough if you want 3D instead of just 1D control. $\endgroup$ Commented Dec 15, 2022 at 17:07
  • $\begingroup$ Add you details in the question so readers do not have to mine the comments. $\endgroup$ Commented Dec 15, 2022 at 20:51
  • $\begingroup$ @StainlessSteelRat Yes, I already added all the details mentioned in my comments to my original question. Thanks for the reminder! $\endgroup$ Commented Dec 16, 2022 at 2:26

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There is no how

The only way to intensify a magnetic field is its current, turns, or geometry of the electromagnet, including core components.

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